As a next-generation wireless LAN standard, WiGig (Registered Trademark) receives attention. The WiGig enables ultrahigh speed wireless communication at up to 6.75 G bits per second via a milli-meter wave of 60 GHz band. Thus, the demand for an antenna for 60 GHz band is considered to increase, because such an antenna is expected to be employed in commercial devices such as personal computers and smartphones, which have a large market size.
A typical example of the antenna for 60 GHz band is an antenna which is integrated with an RFIC. This is because that a high frequency signal of 60 GHz band is not suitable for wired transmission via a coaxial cable, since such a high frequency signal is easy to be attenuated. An antenna module including an antenna for 60 GHz band and an RFIC in an integrated manner is disclosed in, for example, Non-Patent Literature 1.
FIG. 5 is an exploded perspective view showing a configuration of an antenna module 5 disclosed in Non-Patent Literature 1. The antenna module 5 includes a first conductor layer 51, a first dielectric layer 52, a second conductor layer 53, a second dielectric layer 54, a third conductor layer 55, and an RFIC 56 which are stacked in this order.
According to the antenna module 5, the first conductor layer 51 and the second conductor layer 53, which face each other via the first dielectric layer 52, constitute a waveguide slot antenna 5A.
The first dielectric layer 52 includes (i) a power feeding pin 521, which serves as a TE mode excitation structure, and (ii) a plurality of posts 522 arranged so as to surround the power feeding pin 521 from four sides. The power feeding pin 521 is a non-through-hole (blind via) (i) extending from an upper surface of the first dielectric layer 52 to an inside of the first dielectric layer 52 and (ii) having an inner wall to which conductor plating is applied. The power feeding pin 521 has a lower end which is not in contact with the first conductor layer 51, and thus the power feeding pin 521 is electrically insulated from the first conductor layer 51. Further, in order to prevent an upper end of the power feeding pin 521 from coming into contact with the second conductor 53, the second conductor layer 53 has an opening (electrical conductor removed part) 531 (i.e., an anti-pad is achieved by a gap between the upper end of the power feeding pin 521 and the second conductor 53). Consequently, the power feeding pin 521 is electrically insulated also from the second conductor layer 53. Meanwhile, each of the posts 522 is a through-hole (i) extending from the upper surface of the first dielectric layer 52 to a lower surface of the first dielectric layer 52 and (ii) having an inner wall to which conductor plating is applied. Each of the posts 522 has (i) an upper end which is in contact with the second conductor layer 53 and (ii) a lower end which is in contact with the first conductor layer 53, and thus the first conductor layer 51 and the second conductor layer 53 are short-circuited to each other via the posts 522. With this arrangement, a region whose six sides are surrounded by the first conductor layer 51, the second conductor layer 53, and a post wall constituted by the plurality of the posts 522 functions as a waveguide 523 that guides an electromagnetic wave (TE mode) excited by the power feeding pin 521.
A high frequency signal outputted from the RFIC is transmitted through a microstripline 5B (described later) as an electromagnetic wave of TEM mode, and is then converted into an electromagnetic wave of TE mode by the power feeding pin 521. The electromagnetic wave is guided through the waveguide 523, and is then emitted outside the waveguide 523 via slots 511 formed in the first conductor layer 51. In contrast, an electromagnetic wave entering the inside of the waveguide 523 via the slots 511 formed in the first conductor layer 51 is guided through the waveguide 523 as an electromagnetic wave of TE mode, and is then converted into an electromagnetic wave of TEM mode by the power feeding pin 521. The electromagnetic wave is transmitted through the microstripline 5B (described later), and is then inputted to the RFIC 56 as a high frequency signal.
In the antenna module 5, the second conductor layer 53 and the third conductor layer 55, which face each other via the second dielectric layer 54, constitute the microstripline 5B.
The third conductor layer 55 is a conductor pattern printed on a surface of the second dielectric layer 54. The third conductor layer 55 includes a signal line 551, a signal pad 552, and a grounding pad 553. The signal line 551 is a linear electric conductor having one end which is connected to an upper end of a power feeding pin 541 formed in the second dielectric substrate 54. The power feeding pin 541 is a through-hole (i) extending from an upper surface of the second dielectric layer 54 to a lower surface of the second dielectric layer 54 and (ii) having an inner wall to which conductor plating is applied. The power feeding pin 541 has a lower end which is in contact with the upper end of the power feeding pin 521 formed in the first dielectric layer 52, and thus the signal line 551 and the power feeding pin 521 are electrically connected with each other via the power feeding pin 541. The signal pad 552 is a square planar electric conductor having a side which is connected to the other end of the signal line 551. Further, the grounding pad 553 is a square planar electric conductor disposed in the vicinity of the signal pad 552 but apart from the signal pad 552. The second dielectric layer 54 includes a grounding via 542 which is formed therein. The grounding via 542 is a through-hole (i) extending from the upper surface of the second dielectric layer 54 to the lower surface of the second dielectric layer 54 and (ii) having an inner wall to which conductor plating is applied. The grounding via 542 has (i) an upper end which is in contact with the grounding pad 553 and (ii) a lower end which is in contact with the second dielectric layer 53. With this arrangement, the second conductor layer 53 and the first conductor layer 51, which is short-circuited to the second conductor layer 53, have the same electric potential (grounding potential) as that of the grounding pad 533.
The signal pad 552 is connected with a signal terminal (not illustrated) formed on a back surface of the RFIC 56. Further, the grounding pad 553 is connected with a grounding terminal (not illustrated) formed on the back surface of the RFIC 56. This arrangement allows, in sending operation, a high frequency signal from the RFIC 56 to be inputted to the waveguide slot antenna 5A via the microstripline 5B. Further, the above arrangement allows, in receiving operation, a high frequency signal supplied from the waveguide slot antenna 5A can be inputted to the RFIC 56 via the microstripline 5B.
Note that, as those exemplified by the waveguide slot antenna 5A shown in FIG. 5, an antenna having a waveguide made of (i) two conductor layers facing each other and (ii) a post wall constituted by a plurality of posts laterally surrounding a region which is sandwiched by the two conductor layers is called a “post wall waveguide antenna”. Such a post wall waveguide antenna is disclosed by, for example, Patent Literature 1. However, in referring to Patent Literature 1, please note the following point. That is, a post wall waveguide antenna disclosed in Patent Literature 1 is not such a waveguide slot antenna that electromagnetic waves are inputted and outputted via slots formed in a single one of the two conductor layers.